See Rare Diseases by First Letter (C)
- CADASIL
- Calciphylaxis
- Camurati-Engelmann Disease
- Canavan Disease
- Capillary Hemangioblastoma
- Carbamoyl Phosphate Synthetase 1 Deficiency
- Carcinoid Syndrome
- Carcinoid Tumor
- Cardiospasm
- Carney Complex
- Carnitine Palmitoyltransferase 2 Deficiency
- Caroli Disease
- Castleman's Disease
- Cat Scratch Disease
- Catastrophic Antiphospholipid Syndrome
- Central Centrifugal Cicatricial Alopecia
- Central Core Disease
- Central Nervous System Lymphoma, Primary
- Central Post-stroke Pain
- Central Serous Chorioretinopathy
- Cerebellar Astrocytoma, Childhood
- Cerebellar Degeneration
- Cerebral Astrocytoma, Childhood
- Cerebral Cavernous Malformation
- Cerebral Palsy Spastic Diplegic
- Cerebral Palsy Spastic Hemiplegic
- Cerebrospinal Fluid Leak
- Cerebrotendinous Xanthomatosis
- Ceroid Storage Disease
- Cervical Dystonia
- Cervical Intraepithelial Neoplasia
- Chagas Disease
- Chanarin-Dorfman Syndrome
- Chandler's Syndrome
- Charcot-Marie-Tooth Disease
- Charcot-Marie-Tooth Disease Type 1A
- Chediak-Higashi Syndrome
- Cherubism
- Chiari Malformation Type 2
- Chikungunya
- CHILD Syndrome
- Childhood Disintegrative Disorder
- Childhood-Onset Schizophrenia
- Cholecystitis
- Cholera
- Cholestasis, Progressive Familial Intrahepatic 3
- Cholesteatoma
- Chondrocalcinosis 2
- Chondrosarcoma
- Chordoma
- Chorea Minor
- Choreoacanthocytosis
- Choriocarcinoma
- Chorioretinitis
- Choroid Plexus Carcinoma
- Choroideremia
- Choroiditis
- Chromophil Renal Cell Carcinoma
- Chromosomal Triplication
- Chromosome 17p Deletion
- Chromosome 5q Deletion
- Chronic Active Epstein-Barr Virus Infection
- Chronic Berylliosis
- Chronic Graft Versus Host Disease
- Chronic Granulomatous Disease
- Chronic Infantile Neurological Cutaneous Articular Syndrome
- Chronic Inflammatory Demyelinating Polyneuropathy
- Chronic Lymphocytic Leukemia
- Chronic Myeloid Leukemia
- Chronic Myelomonocytic Leukemia
- Chronic Myeloproliferative Disorders
- Chronic Neutrophilic Leukemia
- Churg Strauss Syndrome
- Chylothorax, Congenital
- Cicatricial Pemphigoid
- Citrullinemia Type I
- Classic Kaposi Sarcoma
- Clear Cell Renal Cell Carcinoma
- CLIPPERS
- Clostridium Difficile
- Clostridium Sordellii
- Cluster Headache
- COACH Syndrome
- Coal Worker's Pneumoconiosis
- Coats Disease
- Coccidioidomycosis
- Cockayne Syndrome
- Cogan's Syndrome
- Cold Agglutinin Disease
- Cold Contact Urticaria
- Collagenous Colitis
- Collecting Duct Carcinoma
- Combined Malonic and Methylmalonic Aciduria
- Common Variable Immunodeficiency
- Compartment Syndrome
- Complete Atrioventricular Canal
- Complex Regional Pain Syndrome
- Cone-rod Dystrophy
- Cone-rod Dystrophy 2
- Congenital Adrenal Hyperplasia
- Congenital Amegakaryocytic Thrombocytopenia
- Congenital Antithrombin Deficiency
- Congenital Aplastic Anemia
- Congenital Central Hypoventilation Syndrome
- Congenital Cytomegalovirus
- Congenital Diaphragmatic Hernia
- Congenital Dyserythropoietic Anemia
- Congenital Dyserythropoietic Anemia Type 1
- Congenital Fiber Type Disproportion
- Congenital Heart Block
- Congenital Hemolytic Anemia
- Congenital Hepatic Fibrosis
- Congenital Herpes Simplex
- Congenital Hypothyroidism
- Congenital Muscular Dystrophy
- Congenital Muscular Dystrophy Type 1A
- Congenital Porphyria
- Congenital Torticollis
- Conn's Syndrome
- Conotruncal Heart Malformations
- Conversion Disorder
- Coronary Artery Aneurysm
- Corticobasal Degeneration
- Cowden Syndrome
- Craniofacial Dystonia
- Craniofrontonasal Dysplasia
- Craniopharyngioma
- Craniosynostosis
- CREST Syndrome
- Creutzfeldt-Jakob Disease
- Crouzon Syndrome
- Cryoglobulinemia
- Cryopyrin-associated Periodic Syndrome
- Cryptococcosis
- Cryptogenic Organizing Pneumonia
- Cryptosporidiosis
- Currarino Triad
- Cushing's Syndrome
- Cutaneous Lupus Erythematosus
- Cutaneous Mastocytosis
- Cutaneous Sclerosis
- Cutaneous T-cell Lymphoma
- Cutis Laxa
- Cyclic Vomiting Syndrome
- Cystic Adenomatoid Malformation of Lung
- Cystic Fibrosis
- Cystic Hygroma
- Cysticercosis
- Cystinosis
- Cystinuria
- Cystosarcoma Phyllodes
- Cytomegalic Inclusion Disease
- Cytomegalovirus Retinitis